Department of Psychology and Behavioural Sciences

TY - JOUR

T1 - Neurotransmitter systems involved in placebo and nocebo effects in healthy participants and patients with chronic pain

T2 - a systematic review

AU - Skyt, Ina

AU - Lunde, Sigrid

AU - Baastrup, Cathrine

AU - Svensson, Peter

AU - Jensen, Troels S

AU - Vase, Lene

PY - 2020/1

Y1 - 2020/1

N2 - The investigation of neurotransmitter systems in placebo and nocebo effects has improved our understanding of these phenomena. Yet, most studies involve healthy participants. Because the pain modulatory system may differ in healthy participants and patients with chronic pain, it is important to investigate the evidence for neurotransmitter involvement in placebo and nocebo effects in each of these populations. PubMed, Embase, and Scopus databases, and the Cochrane Library were searched for articles investigating the endogenous opioid, endocannabinoid, dopaminergic, oxytocinergic, vasopressinergic, and cholecystokininergic (CCKergic) systems in placebo and nocebo effects in pain. Twenty-eight placebo and 2 nocebo studies were included. Vote counting was used to balance the number of positive vs negative findings. In healthy participants, the endogenous opioid, endocannabinoid, and vasopressinergic systems were involved in placebo effects, whereas findings on the dopaminergic and oxytocinergic systems were mixed. In patients with chronic pain, only 4 studies investigated neurotransmitters showing no involvement of the endogenous opioid system and mixed findings regarding the dopaminergic system. As to nocebo effects, 2 studies suggest that the CCKergic system is involved in nocebo effects in healthy participants. Overall, research has come a long way in specifying the neurotransmitter systems involved in placebo effects in healthy participants. Yet, evidence for the involvement of neurotransmitter systems in placebo effects in patients with chronic pain and in nocebo effects in healthy participants and patients is scarce. Based on the existing evidence, this systematic review suggests that knowledge obtained in healthy participants may not necessarily be transferred to chronic pain.

AB - The investigation of neurotransmitter systems in placebo and nocebo effects has improved our understanding of these phenomena. Yet, most studies involve healthy participants. Because the pain modulatory system may differ in healthy participants and patients with chronic pain, it is important to investigate the evidence for neurotransmitter involvement in placebo and nocebo effects in each of these populations. PubMed, Embase, and Scopus databases, and the Cochrane Library were searched for articles investigating the endogenous opioid, endocannabinoid, dopaminergic, oxytocinergic, vasopressinergic, and cholecystokininergic (CCKergic) systems in placebo and nocebo effects in pain. Twenty-eight placebo and 2 nocebo studies were included. Vote counting was used to balance the number of positive vs negative findings. In healthy participants, the endogenous opioid, endocannabinoid, and vasopressinergic systems were involved in placebo effects, whereas findings on the dopaminergic and oxytocinergic systems were mixed. In patients with chronic pain, only 4 studies investigated neurotransmitters showing no involvement of the endogenous opioid system and mixed findings regarding the dopaminergic system. As to nocebo effects, 2 studies suggest that the CCKergic system is involved in nocebo effects in healthy participants. Overall, research has come a long way in specifying the neurotransmitter systems involved in placebo effects in healthy participants. Yet, evidence for the involvement of neurotransmitter systems in placebo effects in patients with chronic pain and in nocebo effects in healthy participants and patients is scarce. Based on the existing evidence, this systematic review suggests that knowledge obtained in healthy participants may not necessarily be transferred to chronic pain.

U2 - 10.1097/j.pain.0000000000001682

DO - 10.1097/j.pain.0000000000001682

M3 - Review

C2 - 31453980

VL - 161

SP - 11

EP - 23

JO - Pain

JF - Pain

SN - 0304-3959

IS - 1

ER -